* Precambrian igneous rocks: These are the oldest rocks on Earth, formed from volcanic eruptions and magma intrusions. They include granite, gabbro, and basalt.
* Metamorphic rocks: Formed from existing igneous and sedimentary rocks transformed by heat and pressure deep within the Earth's crust. Examples include gneiss, schist, and quartzite.
It's important to note that the Canadian Shield does contain some sedimentary rocks, mainly in the form of younger layers deposited on top of the older igneous and metamorphic rocks. However, the vast majority of the Shield's composition is made up of the igneous and metamorphic rocks mentioned above.
